1. Field of the Invention
An aspect of the present invention relates to a downward type micro electro mechanical system (MEMS) switch and a method for fabricating the same. More particularly, an aspect of the present invention relates to a downward type MEMS switch and a method for fabricating the same in which a contact pad, which is actuated downward by piezoelectricity, is produced to share a layer with a radio frequency (RF) signal line, after forming a RF signal line.
2. Description of the Related Art
A reconfigurable antenna changes the characteristic of antenna such as center frequency, bandwidth, and gain according to a mechanical or electrical method, and recently, it applies to fabrication of a multi band antenna. If the multi band antenna is applied to a mobile communication device, the mobile communication device should include a switch to divide signals of a frequency bandwidth.
Switches for a conventional reconfigurable multi band antenna include a semiconductor switch, an electrostatic actuation switch, which is actuated by electrostatic force, and a cantilever switch.
In the case of a semiconductor switch, it is difficult to integrally fabricate the semiconductor switch and the antenna on an identical substrate since there occur problems related to fabrication compatibility between the semiconductor switch and an antenna.
An electrostatic actuation switch is generally fabricated by micro electro mechanical system (MEMS) technology and accordingly, a part of the substrate employs a metal. Therefore, electro magnetic coupling phenomenon may probably occur between the metal of the antenna and the metal of the substrate. Thus, there is a limit to the increase in performance, fabrication and design, and there is also a limit to miniaturization and low voltage actuation.
In the case of a cantilever switch, which is mainly used in a piezoelectric scheme, initial displacement may easily occur due to a stress generated when a multi layer is fabricated, and the initial displacement restricts accurate switching controls.
The cantilever switch has a driving layer at one side and accordingly, has less driving force than MEMS switch that drives at both sides so that the cantilever switch has insufficient contact force. Additionally, the driving force of the cantilever switch is reduced due to its unsymmetrical structure.
Additionally, in the case of a conventional MEMS switch driving at both sides, a contact metal contacting an antenna line is formed before an actuator is fabricated so that a coupling phenomenon increases.